# Calculus Rotations Help!!!!

• May 20th 2009, 08:25 AM
Cat27
Calculus Rotations Help!!!!
Hello, I'm am really suck on these problems. If you're really smart I could use your help right now!

Use the disk method to find the volume of the solid:
y=2x-1, x=0, y=x^2 rotated about line y=3

Use the disk and shell method to solve this rotation:
y=-x^2+16, Y=16, X=4 about line x=2

Use either method to solve this rotation:
y=cos(x), y=sin(x), x=pi/4, x=5pi/4, about line x=5pi/4

Please help. I've been working on then for hours and have some equations but I don' know if they are right!(Crying)
• May 20th 2009, 09:03 AM
Kaitosan
Quote:

Originally Posted by Cat27
Hello, I'm am really suck on these problems. If you're really smart I could use your help right now!

Use the disk method to find the volume of the solid:
y=2x-1, x=0, y=x^2 rotated about line y=3

Use the disk and shell method to solve this rotation:
y=-x^2+16, Y=16, X=4 about line x=2

Use either method to solve this rotation:
y=cos(x), y=sin(x), x=pi/4, x=5pi/4, about line x=5pi/4

Please help. I've been working on then for hours and have some equations but I don' know if they are right!(Crying)

I'm going to do the last one only and leave the other two for others.

Ok, here's what I think the integral should be:

$2piINTEG: (sinx-cosx)(5pi/4 -x) dx$ with limits from x=pi/4 to x=5pi/4
• May 20th 2009, 01:52 PM
Cat27
thanks for the help! I solved the others in class already. It just took a little longer than I thought to get to the solutions.